PAL's 4% Speedup

Have you ever watched a movie on TV or VHS or DVD and
enjoyed the music so much that you went and bought the soundtrack CD? Have
you then noticed that the soundtrack CD sounds a bit different to the movie?

Have you ever watched a movie on TV or VHS or DVD
and then found out that the US version is longer than the Australian version?

Have you ever compared the specifications of a DVD
in Australia with a DVD in the US and noticed that the US version runs
longer than the Australian version?

Are we being ripped off? Are our movies censored?

The short answer is no. It is true that the running
times of movies on TV, VHS and DVD are shorter than their theatrical running
times, but this is not because of censorship. It is because of the way
in which movies are transferred to video.

24 Frames Per Second

Movies are projected at 24 frames per second. 24 full
images are projected off the film onto the screen every second. This is
a world wide standard. This is all well and good, but a problem arises
when we want to transfer a movie to video.

50 Fields Per Second

The PAL TV system shows images at 50 fields per second.
One half of an image is displayed and then the other half of the image
is displayed. The nett result of this is that 25 full images are shown
per second.

24 Into 25 Doesn't Go

How do you take a film which has 24 full images per
second and display this on a TV which shows 25 full images per second?
There are two ways you can do this.

The first way, which is not commonly used, is to
show 24 images from the film on the TV in sequence and then repeat the
24th film image. This fits film's 24 images into the 25 images needed by
TV. This approach has one major drawback, which is that once every second
there is a noticeable pause (judder) in the video because of the
extra inserted image. Most people find such an artefact extremely objectionable.

The second way, which is commonly used, is to show
25 images from the film every second. This fits the film nicely into the
TV format of 25 full frames per second, but the nett result is that 25
frames from the film are being shown in the same time as 24 frames were
supposed to have been shown. This means that the film is being shown 4%
faster than it was originally intended to be shown. This approach also
has a series of disadvantages, but these are less objectionable than the
judder introduced with the first-mentioned approach.

Effects of the 4% Speedup

The most obvious effect of this 4% speedup is that the
film runs for 4% less time. Take as an example the recent movie The
Mask of Zorro. The theatrical running time for this movie was 136 minutes
according to the Internet Movie
Database. The running time of this movie on Region 4 DVD is 132 minutes,
4% less.

A less obvious effect of this 4% speedup is that
the audio for the film is both 4% faster and 4% higher in pitch. In musical
terms, this equates to a rise in pitch of a little under one semitone.

Another less obvious effect of this 4% speedup is
that the on-screen action occurs 4% faster.

For the majority of us, this 4% speedup is of no
consequence, and is something that we are blissfully unaware of. For a
small minority of movie and music buffs, the 4% speedup is objectionable.

What Can Be Done About It?

There is very little that can be done about this issue
at present.

One possible partial solution is for the movie's
soundtrack to be digitally processed so that it plays back at the correct
pitch on video. This can be done either whilst the movie is being mastered
for video or whilst the movie is playing back. This is very rarely done
in practice, as it does not solve the problem of the movie and the music
still playing back 4% too fast, even if it is now at the correct audio
pitch.

The advent of DVD and digital projection devices
has opened up another possibility to solve this problem. In theory, a DVD
player could be constructed which plays back PAL movies at the correct
speed and hence at the correct pitch. At present, the only devices capable
of doing this are DVD-ROM drives. Such a device could be mated with a display
device that is capable of displaying images at 24 frames per second. It
is likely that in the future such solutions to this problem will become
more readily accessible, particularly with the advent of HDTV.

Does It Really Matter?

For most of us, the answer is no. However, it is important
to be aware of this issue so as to more fully appreciate the movie watching
experience, and to explain some apparent anomalies in movie running times
that may have troubled you in the past.